1. Field of the Invention
The present invention relates to a control device for power conversion, and more specifically to a dual-mode switching power control device that dynamically controls a flyback converter to perform DCM (Discontinuous Conduction Mode) or CCM (Continuous Conduction Mode) based on a loading state.
2. The Prior Arts
Different electronic devices require specific electric power to operate. For example, ICs (integrated circuits) are supplied with 5V, 3V or 1.8V, electric motors need 12V DC, and high power devices require 110V or 220V AC, like city power. In particular, the lamp of the LED display usually operates at even much higher voltage. Thus, many kinds of electric converters have been developed to meet those various demands.
Flyback converters, which have advantages of simple architecture and wider range of adjustable voltage, are one of the most used switching power converters. As a result, flyback converters are often applied to electronic products consuming medium or small power. Specifically, flyback converters employ switching elements to control the current flowing through the electric transformer so as to generate the output power as desired. At the same time, passive resistor capacitor diodes (RCD) are used to reduce the voltage stress of the switching elements and effectively absorb voltage surge generated by the electric transformer due to leakage inductance.
In the prior arts, Quasi-Resonant (QR) technology is often utilized in flyback converters to reduce switching loss of the switching element by zero voltage and/or zero current switching process such that the efficiency of power conversion is increased. QR generally needs to operate in Discontinuous Conduction Mode (DCM) to drive the switching element so as to effectively reduce the inductance. Furthermore, EMI (electromagnetic interference) can be greatly suppressed by zero voltage and/or zero current switching, and valley switching. The stability of electric operation is thus improved. More specifically, in DCM, the switching element is driven and turned on when the first side current of the electric transformer reduces to zero. Alternatively, Continuous Conduction Mode (CCM) can be used to achieve the same function by turning on the switching element before the first side current of the electric transformer reduces to zero, that is, the first side current is continuous and never reduced to zero.
However, one shortcoming in the prior arts is that higher current spikes and RMS (root-mean-square) values are caused in QR flyback converters operating in DCM. It thus results in higher conduction loss and turn-off switching loss in heavy loading such that the efficiency of power conversion is reduced. Therefore, QR flyback converters operating in DCM are not suitable for higher power applications. Additionally, current power converters use various fixed preset modes or only one mode as the operating mode, and it is not possible to adjust or change the operating mode or operating parameters for different electric transformers and other elements such that the best efficiency is attained.
Therefore, it is greatly needed to provide dual-mode switching power control device, which is implemented by digital design and applicable from light to heavy loading, in particular can automatically determine the loading state and dynamically switch to DCM or CCM based on the loading state so as to improve the efficiency of power conversion, thereby overcoming the above problems in the prior arts.